I focused on buying relatively inexpensive parts. I looked for components which I knew would sell for at least double on eBay, and which I suspected would sell for many times more. For example: I bought a lightly used XTR Rapid Rise rear derailleur for $15. It would eventually sell for $76. Not all of the deals can be that good, but that's the kind of thing I was looking for. I'm not above lowballing people, because hey... a lot of times it works.
I did well. Super well. I left with a few boxes of densely packed gold. I probably could have done much better, but I feel no dismay. A person can usually do better, and that goes for all situations. I had a great time.
My mission today - in no part - included buying a tandem. But I saw an amazing tandem that seemed tailor made for me. Plus, it was powdercoated in bright pink. We bargained back and forth and arrived at $600. I'll profit much more than that from my work today, and hey - who needs all this justification, anyway? I handed him the money and I was riding it around solo and having a ball. If it doesn't get used enough, I'll just sell it for more.